1. Field of the Invention
This invention relates to connecting elements for components of mechanical assemblies and in particular, to connecting keys.
2. Description of the Prior Art
Key connection conventionally consists of a key engaged with slots or other recesses fabricated in the mating surfaces of two components being joined. In some cases, to improve concentricity and/or increase load-carrying capacity of power-transmission joints, multiple keys or their modification--a spline connection is used.
Due to inevitable tolerances of keyslot dimensions in both components to be connected and of the key itself, usually the key is pressfitted in one component's keyslot and loose in another component's keyslot. The interference fit in the first said keyslot should not be too tight because of possible assembly/disassembly difficulties, thus the key has to be machined during the assembly, especially for maintenance purposes. A loose fit leads to inevitable backlashes which may cause high impact loads leading to further loosening and deterioration of the key.
A conventional keyslot (e.g. for square or Woodruff key) has sharp inside corners causing stress concentration and crack generation both in the shaft and sleeve. Making generous fillets and special key shapes to reduce stress concentration, such as Orthwein teaches in U.S. Pat. No. 3,920,343, requires more complicated tooling, more expensive keys and also reduces load carrying and guiding areas of the keyslot thus necessitating making it deeper. But even a conventional keyslot substantially weakens a component crossection, and the modified keyslot weakens it to a greater degree.
In many cases, heat treatment (hardening) of the slotted portion would greatly improve the load carrying capacity (fatigue and/or wear resistance) of the whole assembly. However, this cannot be done neither before cutting the keyslot because of impaired machining conditions nor after the keyslot had been cut because inevitable distortions would make key fit procedure difficult or even impossible.
Prior methods were proposed to reduce backlash and increase load carrying capacity of a key connection, e.g. by using cylindrical key inserted in a hole having been drilled in the contact area of two components being connected, at the time of assembly. However, this requires more skilled labor for the assembly process and also makes repair difficult after the initial keyslots had worn out and changed their dimensions and shape.